Talk:Equinox

Southern hemisphere

We need to edit this article so that it is not Northern hemisphere-centric, as per the comments in the lead. Is there anywhere in the Southern hemisphere that uses the term 'Fall equinox', maybe even as a translation in the local language, or is it always 'Autumnal equinox'? If someone could clarify this point I'll do the edits. Silas Stoat (talk) 19:36, 18 March 2019 (UTC)

Explanation of the oscillation of the date of the equinox

Jc3s5h's observation that "Nobody ever observed the equinoxes as if they were calculated" etc. is irrelevant. Obviously if you observe the equinox you're not calculating it. Nobody has suggested that anyone ever did this. I'm happy to remove the StackExchange cite as the other one is adequate. 81.139.160.225 (talk) 18:00, 22 March 2019 (UTC)

The date and time of the equinoxes and solstices are often obtained from the Astronomical Almanac for the year in question. Those who need an authoritative source before the relevant almanac is published can consult the website of the United States Naval Observatory or Her Majesty's Nautical Almanac Office, who lead the team who prepare the almanacs, and are listed on the title page.

The procedure for calculating the equinoxes and solstices are specified on the Explanatory Supplement to the Astronomical Almanac 3rd ed. edited by Sean E. Urban and P. Kenneth Seidelmann. (Mill Valley CA: University Science Books, 2013).

From "12.2.1.1 Equinoxes and Solstices" p. 506

The times of the equinoxes and solstices are defined to be when the Sun's apparent ecliptic longitude λ_S is a multiple of 90°; i.e., it is calculated from f(t) = 0 where f(t) = λ_S - 0°, 90°, 180°, or 270°.

The calculation procedure given on page 508–9 agrees with this definition.

The passage inserted by 81.139.160.225 (talk · contribs) was placed in the lead of the article, which is intended as an overview of the topic. A diversion into some alternate calculation used in an almanac from a Maine farmer's almanac has no place in the article, and especially not in the lead. Jc3s5h (talk) 18:30, 22 March 2019 (UTC)

In the original edition of this article Karl Palmen stated that the "equinox occurs on March 19, 20 or 21." Are you saying that Karl's observation that the equinox might fall on 19 March was wrongly "placed in the lead of the article, which is intended as an overview of the topic"? If you are not saying that, why are you objecting to the readers being informed that an equinox can happen as late as the 23rd or 24th of the month, as indeed happens with the autumnal equinox at the present time? 81.139.160.225 (talk) 17:35, 23 March 2019 (UTC)

In these edits 81.139.160.225 (talk · contribs) substantially restored '225's previous edits, which I had removed due to errors, unsuitability for the lead, and, and poor sources. I will now show the numerous problems with this passage in detail.

The added passage is

The dates are variable, dependent as they are on (1) the leap year cycle and (2) the longitude of the perihelion. In 1939 the dynamical mean sun crossed the equator at 10:11 AM (GMT) on 23 March.

The first sentence claims the dates are variable because of the leap year cycle and the longitude of the perihelion. While the variability due to the leap year cycle is described in numerous reliable sources, the dependence on the longitude of perihelion is cited to a popular article from 1930. On the page cited, 579, there is no discussion of the variability of the date of the equinoxes, or is that the topic of the article. Thus no reliable source has been provided to verify that the longitude of the perihelion is the second-most-important cause of variability in the date of the equinoxes.

The second sentence gives the date the dynamical mean Sun crossed the equator in March 1939. But the equinox occurs at the time the apparent celestial longitude of the Sun is 0° or 180°. The date and time the fictitious mean Sun, a.k.a. dynamical mean Sun (formerly used in the calculation of mean time) crosses the equator is not generally of interest in astronomy and will not be found in reliable sources such as the US Naval Observatory website nor in the Astronomical Almanac. The source is a Sky and Telescope about the meaning of the phrase "blue moon". That article dredges through obscure sources to try to figure out where the phrase came from, and is not relevant to the topic of this article. Jc3s5h (talk) 17:32, 24 March 2019 (UTC)

I have added a subsection, "Modern dates", which describes the variability and provides a citation to a reliable source, the Explanatory Supplement to the Almanac 3rd ed. I believe this is more appropriate than adding material to the already-long lead. Jc3s5h (talk) 17:53, 24 March 2019 (UTC)

This is most unsatisfactory, since the source quoted is not publicly available. However, doing the best I can, the mean sun formerly used in the calculation of mean time has nothing whatsoever to do with calculating the equinox. It circles the equator, while the dynamical mean sun circles the ecliptic. Since Jc3s5h does not understand this crucial difference he has said that the date of the equinox varies "slightly", when it actually varies by 2d 5h + 1d 22h + 1d 22h, which adds up to a whopping 6d 01h. So the current version of the article is wrong. 81.139.163.204 (talk) 12:12, 27 March 2019 (UTC)

The date and time that 81.139.163.204 represents as the 1939 March equinox, 23 Th 10h 11m eve., is taken from a copy of part of a page from the 1939 Maine Farmer's Almanac which appears in an article in Sky and Telescope by Olsen et al. They write, in the box containing the Maine Farmer's Almanac that "These tables appeared in the 1939 Maine Farmers' Almanac and show that the beginnings of the seasons were fixed by the 'R.A.M.S.' (right ascension of the mean Sun)." Outside the box, in the main text of the article, a few lines later, the Olsen et al. write "Today we usually mark the beginning of the seasons when the Sun's celestial longitude passes 0° (spring), 90° (summer), 180° (autumn), and 270° (winter)." So your own source agrees with this Wikipedia article was written before your changes. Jc3s5h (talk) 12:56, 27 March 2019 (UTC)

You appear to have a competence problem if you can't work out the difference between the start of equal seasons which the writers expressly state are NOT the beginning of seasons as they are generally understood and equinox and solstice times as provided by, for example, the Royal Greenwich Observatory. 81.139.163.204 (talk) 13:24, 27 March 2019 (UTC)

References

Incorrect perspective for "File:Earth-lighting-equinox_EN.png"

The files in Solstice show the axis tilt lighting correctly alone with the perspective of someone on the orbital plane or ecliptic. The ones here should match the perspective as to not confuse viewers. The perspective with Earth-lighting-equinox_EN shows the lighting above the equator and the sun at a right angle (not the same as the orbital plane). Can someone please correct. John W. Nicholson (talk) 21:03, 27 March 2019 (UTC)